So far, when the oil drilling is carried out by the use of a drill, in order to magnetically detect a position of a drill at a leading end from on an earth surface to specify and control the position, a measurement device is installed in a drill collar close to a bit. At that time, in order to measure the orientation and inclination, since the earth magnetism has to be inhibited from affecting thereon, a nonmagnetic steel has to be used in the drill collar.
So far, in such an application, a high Mn nonmagnetic stainless steel such as 13Cr-18Mn-0.5Mo-2Ni-0.3N or 16.5Cr-16Mn-1Mo-1.3Ni-0.5Cu-0.4N has been used. Furthermore, various kinds of nonmagnetic stainless steels that are improved in terms of the corrosion resistance, the stress corrosion cracking, the strength, and the toughness as well as the nonmagnetism have been developed as well.
For instance, JP-A-05-195155 discloses a retaining ring material for the power generator which is constituted of a nonmagnetic iron-base alloy that contains, by weight percent, C: 0.04 to 0.06%, Mn: 19.39 to 19.83%, Cr: 19.68 to 20.12%, N: 0.616 to 0.674%, Mo: 1.44 to 1.62%, Ni: 0 to 2.97%, REM: 0 to 0.062% and the remainder being Fe and inevitable impurities.
This document describes that when a composition is set like this, the toughness and the corrosion resistance can be improved without damaging the strength.
Furthermore, JP-A-05-105987 discloses a retaining ring material for a power generator which is constituted of a nonmagnetic iron-base alloy that contains, by weight percent, C: 0.04 to 0.06%, Si: 0.49 to 0.58%, Mn: 19.38 to 19.87%, Ni: 0 to 2.83%, Cr: 19.65 to 20.18%, N: 0.612 to 0.705%, REM: 0.005 to 0.072% and the remainder being Fe and inevitable impurities.
This document discloses that when the REM is added, the toughness is inhibited from deteriorating.
Still furthermore, JP-A-60-13063 discloses an austenitic stainless steel for use in a very low temperature structure, which contains, by weight percent, C: 0.02 to 0.03%, N: 0.34 to 0.44%, Si: 0.48 to 0.70%, Cr: 16.5 to 22.0%, Ni: 9.0 to 17.5%, Mn: 4.5 to 13.2% and the remainder substantially being Fe, wherein Cr+0.9Mn satisfies 26.1 to 30.9% and the cleanness is in the range of 0.021 to 0.054.
This document describes that, when Cr and Mn are added in combination, the solubility of N may be increased and, when N is interstitially dissolved, the proof stress and toughness at very low temperature may be improved.
Furthermore, JP-A-59-205451 discloses a high-strength nonmagnetic steel obtained by subjecting, to a heat-treating and processing under prescribed conditions, a steel ingot that contains C: 0.057 to 0.135%, Si: 0.21 to 0.50%, Mn: 9.50 to 20.10%, Ni: 0.90 to 5.80%, Cr: 19.98 to 21.00%, Mo: 0.05 to 2.15%, N: 0.408 to 0.640% and the remainder substantially being Fe.
This document describes that, when, after the hot forging is applied, a processing is conducted at a temperature of 1000° C. or more at a processing rate of 10% or more, grains are fined and, when the processing is further conducted at a temperature in a range of 600 to 1000° C. at a processing rate of 10% or more, grains are fined and a carbonitride is precipitated finely.
Still furthermore, JP-A-61-183451 discloses a high-strength nonmagnetic steel that contains, by weight percent, Mn: 24.6 to 28.1%, Cr: 17.5 to 18.3%, V: 1.08 to 1.57%, C: 0.09 to 0.12%, N: 0.42 to 0.66%, Mo: 2.1 to 3.2%, Ni: 3.6 to 5.4% and the remainder being Fe and accompanying impurities.
This document describes that, when alloy elements are optimized, a nonmagnetic, high-strength and high corrosion resistance member is obtained.
Still furthermore, JP-A-61-210159 discloses a control rod driving unit for use in a nuclear power plant, which is constituted of an alloy containing, by weight percent, C: 0.09 to 0.12%, Mn: 24.6 to 28.1%, Cr: 17.5 to 18.3%, Ni: 3.6 to 5.4%, Mo: 2.1 to 3.2%, V: 1.21 to 1.57%, N: 0.42 to 0.66% and the remainder being Fe and accompanying impurities.
This document describes that, when alloy elements are optimized, the wear resistance and the corrosion resistance may be improved without the necessity of adding Co.
In the above-mentioned various kinds of nonmagnetic stainless steels, when alloy elements are optimized, the strength and the corrosion resistance may be improved to some extent. However, recently, demands for petroleum has been very strong and drilling areas has been various. Furthermore, a deeper drilling depth has been also demanded. Accordingly, for these applications, materials having higher strength and higher corrosion resistance has been demanded.
Furthermore, in general, as a material is made higher in the strength, the workability thereof tends to be poorer. However, in order to reduce the production costs of the various kinds of parts, the workability has to be improved while maintaining the high characteristics.